FIX API with Hedged Accounts

Hey,

I've been able to get FIX API to work with Netting Accounts, however, I now need to use a hedged account.

How can I do this, what changes or tags do I need to use to buy and sell similarly to a netting account.

I have tried to use the tag: 721 - PosMaintRptID, but when trying to sell on a long position or buy when in a short position, it doesn't work.

Thanks.